Key words tumor; tumor stem cells; cancer treatment

The original oncogene Her  also known as C  erbB  2 or of Her  2/neu human epidermal growth factor receptor (EGFR) family members, is located on chromosome 17q21, encoding 255 amino acids with a transmembrane tyrosine kinase activity of growth factors, including the extracellular ligand binding functional area and the interior of the cell having a tyrosine kinase activity portion and the transmembrane region, the receptor is a molecular weight of approximately 185KD, it is also known of p185 [ 1]. Despite of Her  2 receptor exact ligand is unclear, but the specific role of ligand in of Her  1, Her-3, Her-4 and other members of the EGFR family, Her  2 can form heterodimers with these members dimers and activate their inner membrane protein fragment containing tyrosine residues, the carboxyl terminus of the tyrosine kinase phosphorylation, Her-2 over-expression of accelerating to promote the proliferation of tumor cells, the degree of malignancy of the cell is enhanced [2] . Has been in the 25% to 30% of breast cancer, ovarian cancer of 10% to 15%, 5% to 10% of gastric cancer, colon cancer, and non-small cell lung cancer in several tumor cell of Her-2 over-expression. Her  2 over-expression of the effects of speed up the promotion of tumor cell proliferation, cell cycle progression, malignant behavior of cells, and anti-apoptotic, and a variety of chemotherapy drug resistance phenomenon [3].

    Herceptin to of Her  2 as a target for a humanized monoclonal antibody to become targeted drug of the first molecule in the field of breast cancer treatment, it is a high purity, recombinant DNA-derived humanized monoclonal immunoglobulin G1 light chain antibody (IgG), specific recognition of Her  2 receptor extracellular domain, inhibition mediated signal transduction, play a role in anti-tumor human epidermal growth factor receptor 2 (Her-2) positive metastatic breast cancer has a good effect. Although the the Herceptin clinical efficacy has been affirmed, but its anti-tumor mechanism of action remains to be further studied. The study found that p27Kip1 may play a certain role in the inhibition of breast cancer cell proliferation process in the Herceptin.

    1 Herceptin Her  2 overexpressing breast cancer patients with treatment mechanism

     Research found that 20% to 30% of breast cancer patients of Her-2 over-expression, Her-2 overexpression indicates a poor prognosis of poor standard chemotherapy and endocrine therapy. Since 1998, the FDA approved Herceptin used in Her  2 overexpressing metastatic breast cancer treatment since its efficacy has been a positive, single-agent therapy overexpression of Her  metastatic breast cancer, the total efficiency of 25% around [2]. Adjuvant chemotherapy after a single agent use Herceptin year, and to extend Her  2 overexpressing breast cancer in patients with disease-free survival time, reduce the risk of recurrence and metastasis and prolong survival, while not significantly improved cardiac toxicity have been published in the 2005 ASCO meeting.

    Clinical studies have confirmed with Herceptin alone, compared with a synergistic combination chemotherapy, paclitaxel, doxorubicin and platinum (cisplatin or carboplatin), to improve the efficacy of chemotherapy drugs. Herceptin combined with chemotherapy can significantly improve the remission rate of breast cancer recurrence and metastasis, and prolong the time to progression of the disease and the patient’s disease-free survival. Herceptin combined with chemotherapy, better safety and tolerability of high [2,4]. 2004, many European countries have Herceptin plus docetaxel as first-line treatment of metastatic breast cancer Her  2 expression.

    Although Herceptin widely used clinically for nearly a decade, however, of Herceptin anticancer mechanism is not yet clear, possible through the following means to inhibit the growth of breast cancer cells Her  2 expression [5]: (1) Her  2 specific binding, blocking ligand-mediated cell signaling, affect the growth of epithelial cells; (2) Accelerated Her  2 receptor internalization and degradation; (3) down Her  2 gene play an anti-proliferative effect; (4) by the ADCC mechanism to improve the ability of immune cells to attack and kill the tumor cells; (5) cut vascular endothelial growth factor and vascular endothelial growth factor, inhibit tumor vascular tissue growth; (6) induction of cyclin-dependent kinase (CDK) inhibitor agent (cyclin  dependent kinase inhibitor, CDKI) cell cycle arrest, promoting apoptosis. The present study, Herceptin may be induced by the tumor suppressor gene p27Kip1 achieve a therapeutic effect.

    2 p27Kip1 participation Herceptin role in the process of

    p27Kip1 is a relative molecular weight of the 27KD heat resistance of the cell cycle inhibitor protein of p27Kip1 gene are mainly located in the short arm of chromosome 12 District 3 band 12p13 contains two exons and two introns, people p27Kip1cDNA long 594bp, encoding 198 amino acids. p27Kip1 by inhibiting the activity of cyclin  CDK complexes, mainly the transition from G1 to S phase of the cell cycle inhibition to block cell cycle progression, belonging to the cyclin-dependent kinase inhibitor. Conversely, cyclin  CDK complexes directly down p27kip1 expression and inhibits its activity to promote cell proliferation. Cyclin  CDK2 make p27Kip1 Thr187 phosphorylation and cause its degradation within the cell, the cell cycle from G1 to S phase.

    P27Kip1 expression levels of axillary lymph node metastasis, and disease-free survival in patients with significant relationships in human breast cancer cells of patients. p27Kip1 expression was higher axillary lymph node metastasis little or no longer, disease-free survival; expression of p27Kip1 expression lower in patients with axillary lymph node metastasis common shorter disease-free survival. The above studies have shown that the level of intracellular p27Kip1 expression is an independent prognostic value indicators. Nahta R, et al [2] found that Herceptin can improve the expression levels of intracellular p27Kip11 to inhibit the proliferation of tumor cells to control the progression of the disease and prolong the survival of patients.

    3 Herceptin raised the expression of p27Kip1 in breast cancer cells, the mechanism of action 3.1 blocks the PI3K/Akt pathway

    Phosphatidylinositol  3-kinase (PI3 K) plays an important role in the regulation of tumor cell signal transduction in tumor cells in a series of internal and external factors, by the start of PI3 K / Akt signaling pathway induced cell proliferation , differentiation, prevent apoptosis. The activation of the PI3K/Akt signaling pathway can lead to downregulation of p27kip1 in specific cells, can promote p27Kip1 protein hydrolysis cells [6].

    Michael Yakes, [7] study confirmed the role of the PI3K/Akt signaling pathway activation occurs mainly at the post-transcriptional stage, Akt phosphorylation of p27Kip1 nuclear localization signal area threonine 157 and 198 threonine. PTEN deletion and Her2 overexpression cells, Akt-mediated phosphorylation of to inhibit p27Kip1 the nuclear translocation, p27Kip1 198 threonine phosphorylation prompted p27kip1 gather and promote its degradation in the cytoplasm. P27kip1 expression levels in the cytoplasm of Akt activation in breast cancer patients have a great relationship [6]. Herceptin and the cell membrane surface of Her  2/neu protein binding blocks the PI3K/Akt pathway by inhibiting Akt phosphorylation of p27Kip1 nuclear localization signal area 157 and 198 threonine to increase intracellular expression of p27Kip1.

    3.2 inhibition of cyclin-dependent kinase 2 (CDK2)

    The process of transcription and post-transcriptional stage, p27Kip1 Expression. However regulation of p27Kip1 the expression at the post-transcriptional stage ubiquitin  proteins to ligase SCFSKP2 pathway is a major mechanism of post-transcriptional stage regulation of p27Kip1 expression. cyclinE  CDK2 phosphorylation modification the p27Kip1 187 threonine phosphorylation of p27kip1  protein ubiquitin ligase SCFSKP2 combination p27Kip1 degradation [8  9].

    The study found that Herceptin is mainly to enhance the stability of p27Kip1 protein to induce the expression at the post-transcriptional stage. In vitro experiments have confirmed that Herceptin and the cell membrane surface of Her  2/neu protein binding phosphorylation by blocking cyclinE  CDK2 the p27Kip1 187 threonine, lower p27Kip1 the  proteins with ubiquitin ligase SCFSKP2 combine to suppress p27Kip1 degradation, Herceptin can extend the half-life of p27Kip1. p27Kip1 protein degradation before the first occurrence of phosphorylation, if blocking its phosphorylation will be able to reduce the degradation of p27Kip1. Therefore, inhibition of cyclinE  CDK2 function is an important mechanism to the Herceptin control p27Kip1 degradation. Herceptin block cyclinE  CDK2 phosphorylation of p27Kip1 187 the threonine channels further research is needed. However, Dipak Das, etc. [10] Recent studies have found that Ras-mediated MAPK signaling pathway to promote p27Kip1 downregulation, Her-2 his family of receptor tyrosine kinases Her  3 of Her  4 form heterodimers trimer, causing of Her  2 carboxyl terminus of the tyrosine residues phosphorylated, its downstream signaling proteins, such as SHC and Grb2 binding to Her  2 src homology region of the protein carboxy terminus. In the inner membrane, SOS SHC and Grb2 interactions that lead to the SOS activated ras, eventually activate MAPK. MAPK activation signal to the nucleus, activating transcription factor c myc, c  fos and c  jun p27Kip1 downregulation, p27Kip1 expression the lowered promote abnormal cell proliferation and differentiation. Her Herceptin and the cell membrane surface  2 protein binding blocking Ras-mediated MAPK signal pathway to increase intracellular p27Kip1 thereby inhibiting abnormal cell proliferation. In short, Herceptin also has raised the tumor suppressor gene p27Kip1 expression suppression function cyclinE  CDK2 and blocking Ras-mediated MAPK signaling pathway.

    3.3 inhibition of nuclear transport protein Jab1/CNS5

    J.Esteva [11] found that in human breast cancer cell nuclear transfer protein Jab1 expression levels than normal mammary epithelial cells, while the amount of p27Kip1 expression. Nuclear transporter protein Jab1 induces p27Kip1 degradation to promote tumor cell proliferation, it is mainly induced p27Kip1 transported from the nucleus to the cytoplasm, and  proteins by ubiquitin ligase accelerated degradation of p27Kip1 in the cytoplasm. Apart Jab1/CSN5 induction p27kip1 degradation, of of of CSN3, CSN6, CSN7 with CSN8 overexpression could also induce the degradation of p27Kip1 in the cytoplasm. Jab1/CSN5 be able to adjust the shuttle movement of p27Kip1 in cells as well as other CSN function, they are induced p27Kip1 degradation in the cytoplasm. Herceptin Her cell surface  2 protein binding reduces breast cancer cell kernel transporter protein Jab1 expression; of Jab1 decreased expression, p27kip1 transported from the nucleus to the cytoplasm to reduce the increased coalescence in the nucleus, and ultimately inhibit tumor cell proliferation. It is found that the 10 serine phosphorylation of p27Kip1 also be able to reduce the expression of the nuclear transport protein Jab1 with Herceptin, which can improve the p27Kip1 10 serine phosphorylation, to further reduce the nuclear transport protein Jab1 expression consistent.

    Studies have shown that p27Kip1 protein interactions with nuclear proteins [11]. Nup50/NPAP60 play an important role in p27Kip1 transported to the nucleus. The two nuclear transporter protein CRM1 with ras  GTP kinase Ran transit between the cytoplasm and the nucleus. 10 p27Kip1 protein serine phosphorylation and nuclear transport protein CRM1 binding before we can be transported from the nucleus to the cytoplasm. Observation of Herceptin on the effect of Nup50/NPAP60 researchers detection experimental results found that Herceptin does not change the Nup50/NPAP60, nuclear transport protein CRM1, and Ran expression by RT  PCR. Thus, Herceptin addition to the role in the nuclear translocation the protein Jab1/CSN5 outside, does not work with other nuclear transporter protein.

    3.4 inhibit the nucleoprotein hKIS function

    p27Kip1 phosphorylation of threonine 187 is able to accelerate the degradation of p27Kip1; able to enhance the stability of p27Kip1 protein phosphorylation of serine 10. All p27Kip1 phosphorylation, 75% of 10 serine phosphorylation, 10 serine phosphorylation of its major phosphorylation sites. Ishida et al [12] study confirmed the nucleoprotein hKIS to phosphorylation of p27Kip1 10 serine phosphorylation of p27Kip1 10 nucleoprotein hKIS, Serine not enhance the stability of p27Kip1 promote from nuclei to the cytoplasm, : ① catalytic nucleoprotein hKIS, phosphorylation of serine 10 can promote the degradation of the tumor suppressor gene p27Kip1 reduce p27Kip1 content in the cells to promote the proliferation of tumor cells; the ② nucleoprotein hKIS overexpression can antagonize the p27Kip1 biological functions, the abnormal cell proliferation and differentiation. When the cell core protein hKIS deletion, p27Kip1 10 serine not phosphorylated, but is able to inhibit cell proliferation. Vitro studies have demonstrated that the combination of Herceptin and the cell membrane surface of Her  2/neu protein, able reduce the cell kernel protein hKIS the expression, thereby reducing hKIS phosphorylated p27Kip1 10 serine, to improve the content of p27Kip1 in the nucleus; through adjustment hKIS inhibit p27Kip1 from the nucleus to the cytoplasm to avoid degradation in the cytoplasm and in the nucleus exerts its biological effects [13].

    3.5 raised MIRK/DYRK1B

    p27Kip1 10 serine phosphorylation is the major phosphorylation sites, about 75% of the total accounting p27Kip1 phosphorylation sites, which have two different phosphorylase acting on the first 10 points. Deng X, et al [14] found that MIRK, DYRK1B serine phosphorylation of p27Kip1 protein 10. Promote the degradation of different p27Kip1 from the nucleus to the cytoplasm MIRK, DYRK1B phosphorylated p27Kip1 protein 10 serine can enhance the stability of p27Kip1 protein not induced p27kip1 nucleus shift with the nucleoprotein hKIS catalytic 10 serine phosphorylation degradation to the cytoplasm. MIRK missing or reduced p27Kip1 protein stability. The growth-stimulating factor able to reduce the expression of MIRK. MIRK through other mechanisms may also regulate the cell cycle changes, Zou X, etc. [15] study found MIRK can and cyclin D1 combination, and promote the 288 threonine phosphorylation of cyclin D1 degradation cell cycle arrest, and to reduce the abnormal proliferation of tumor cells, differentiation.

    Regulating p27Kip1 protein serine 10 phosphorylation process, Mirk and hKIS the opposite role [14]. ① the mitogen activation hKIS, but can not activate MIRK. The ② MIRK in the G0 phase of the cell cycle of the highest expression levels and activity, and degradation in the G1 phase; HKIS expression levels and activity gradually increased in the G1 phase. (3) 10 hKIS catalytic serine phosphorylation promote tumor suppressor gene p27Kip1 degradation from the nucleus to the cytoplasm, and 10 MIRK phosphorylated p27Kip1 protein serine to enhance the stability of p27Kip1 protein. In addition to the above effects, Mirk and hKIS may have other different role. The Herceptin and the cell membrane surface, the Her  2/neu protein binding to promote intracellular MIRK expression, this conclusion is also proved the Herceptin able to improve p27Kip1 10 serine phosphorylation. By inhibiting the hKIS and activated MIRK of, Herceptin induced serine phosphorylation of p27kip1 10 prevent its nuclear Sinotrans, and the ability to enhance the stability of the nuclear p27Kip1 protein.

    3.6 inhibit cyclin-CDK oncogene c  myc expression

    Is a non-specific tumor suppressor gene p27Kip1 CDKI, inhibit many different CDK complexes, but the main suppression by cyclin E-CDK2 and cyclin D  of CDK2 in G1 phase kinase complex. Research shows that cyclinE  CDK2 and of cyclinD  of CDK2 is cell cycle catalytic cells from G1 phase to enter the S phase of the key enzymes, expression of p27Kip1 protein mainly through inhibition of folding seed composite material of so cells stagnation in the G1 phase, so as to achieve the regulation of cell cycle function. p27Kip1 inhibition of the CDK has two aspects: (1) can be suppressed has been activated cyclin CDK kinase activity; ② is also possible to suppress the the CDK activation process [4,7].

    Suldan [16] study found that by the oncogene c-myc can inhibit the activity of p27Kip1. c  myc expression inactivated enhanced prevents cyclin of E  CDK2 activity, allowing the cells to continue to proliferate in the presence of p27Kip1, c  myc in this process, neither change cyclin E  CDK2 inhibition of p27Kip1 easy sensibility, only induced p27Kip1 exists in the form of one kind can not be combined with cyclin E  CDK2, accumulate in the cells. Oncogene c  myc at the transcriptional level by activating the ubiquitin  the protein ligase SCFSKP2 suppress the the p27Kip1 the function while promoting its degradation by the oncogene c-myc and Ras in cells within the co-expression of cells within the tumor suppressor gene p27Kip1 can disappear . O’Hagan et al [17] found that of Her to activate Ras  MAPK pathway, can promote the expression of the cyclin D-oncogene c myc, thereby promoting p27Kip1 degradation of intracellular  signal transduction process. Blocking the Ras  MAPK pathway, cyclin D-oncogene c  myc expression will be lowered. Of Her  2 overexpression can enhance the activity of the cyclin D through the activation of Ras  MAPK (ERK, c  Jun, JNK, p38) pathway.

    It has been proved the Herceptin able to inhibit the cyclin D-oncogene c myc expression. Herceptin and the cell membrane surface the Her  2/neu protein binding play a pharmacodynamics First of suppression by the oncogene c-myc expression, and then inhibit the expression of cyclin D, inhibition of cyclin D expression slower process. In short, Herceptin can be suppressed tone more than the expression of the cyclin D-oncogene c myc cells p27Kip1 also combined inhibition of the p27Kip1 CyclinE  CDK2 complexes.

    4 Conclusion

    Domestic and foreign scholars for the mechanism of action of Herceptin has been doing a lot of research, but the exact mechanism has yet to be further explored. Herceptin raised recently over-expression of Her mechanism of of p27Kip1 the  breast cancer cells to become a research hotspot. It has been found that Herceptin may be provided by the several different ways to maximize the intracellular p27Kip1 expression to inhibit tumor cell proliferation, differentiation purposes. Therefore, this discovery so that people have a better understanding of the mechanism of action of Herceptin, while the application also provides more options for the treatment of HER2-positive breast cancer patients.